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SEARCH HUU'I' Oct. 20, 1970 R, F, BENTLEY EI'AL Re. 26,970

METHOD AND APPARATUS FOR TRANSLATING CUTTING TOOL. MOVEMENT OriginalFiled July 25, 1961 /5 M421@ j IN1/amok:

` HTTZ/YEV United States Patent O 26,970 METHOD AND APPARATUS FORTRANSLATING CUTTING TOOL MOVEMENT Robert F. Bentley, Hudson, Ohio, andSam V. Simonetti, Harper Woods, Mich., assignors to General MotorsCorporation, Detroit, Mich., a corporation of Delaware Original No.3,135,852, dated June 2, 1964, Ser. No. 126,624, July 25, 1961.Application for reissue Mar. 7, 1966, Ser. No. 534,622

Int. Cl. B23p 1/08, I/12 U.S. Cl. 219-69 21 Claims Matter enclosed inheavy brackets [Il appears in the original patent but forms no part ofthis reissue specilication; matter printed in italics indicates theadditions made by reissue.

ABSTRACT F THE DISCLOSURE T o eect translarory movement between anelectroerosion machining electrode and a workpiece, a rotating input iseccentrically mounted to drive the electrode in an orbital path. am! asliding yoke is connected with the electrode to prevent electroderotation and allow electrode translation.

This invention relates generally to machine tools and particularly to adevice for correlating movements between a cutting tool and'workpece.The device is adapted for use, although not exclusively, with electricalstock removal apparatus.

The machining of noncircular contours and tapers with a rotary powersource presents the problem of correlating relative movements betweenthe cutting tool and the workpiece in order to achieve the desiredresult. One example of this occurs with the well known process employingthe electrical stock removal apparatus and commonly referred as toElectrical Discharge Machining. In this process a series of electricaldischarges are generated across an ionizable fluid-filled gap formedbetween cutting tool and workpiece electrodes. These electricaldischarges cause stock to be eroded from the workpiece electrode inaccordance with a certain scheme usually determined by the contour ofthe cutting tool electrode. The process has been found to be veryadvantageous in the machining of irregular configurations in hardenedmaterials, such as used for dies and punches. But the process doespresent problems when close dimensional control is demanded, for thecutting tool electrode normally wears in a way that produces a taper,which may be objectionable, on the workpiece electrode as the machiningtakes place. Also, if for some reason it is desired to alter the size ofa machined surface, the cutting tool electrode used to machine in thefirst instance often cannot be reused, but an entirely new cutting toolelectrode is required for the new dimensions. Moreover, if a specifictaper is needed, e.g., a certain draft angle may be required, the taperdue to the normal wear of the cutting tool electrode complicates theproblem.

Accordingly, the invention contemplates a novel mechanism for convertingthe rotary movement of a power source into relative translatory movementbetween a cutting tool and a workpiece. Specifically, the arrangementproduces oscillatory movement in all directions. This permits anoversize female cutting tool to be utilized for machining of a maleworkpiece to a smaller size. Similarly, an undersize male cutting toolmay be employed to increase the dimensions of a female workpiece.

The invention further contemplates provision of a unique system thatenables a certain taper to be machined or the sides of a machinedsurface to be made relatively straight.

Re. 26,970 Reissued Oct. 20, 1970 More particularly, the invention seeksto adapt the foregoing system for use with the EDM process by convertingthe rotary motion of a power source into translatory movement of one ofthe electrodes such that oversize female cutting tool electrodes andundersize male cutting tool electrodes can be utilized respectively tomachine male and female workpiece electrodes to accurate size whilepermitting the sides of the surfaces machined in a workpiece electrodeto be tapered or made straight.

Another aim of the invention is the provision of a novel control systemfor enabling synchronism of the relative movement between a cutting tooland a workpiece to facilitate the generation of different types ofsurfaces and shapes.

The foregoing and other objects and advantages of the invention will beapparent fgoxlf the following description and the accompanying drawingsin which:

FIG. 1 is a plan view of two electrodes employed by EDM apparatusincorporating the principles of the invention;

FIG. 2 is a sectional view taken along line 2-2 of FIG. 1:

FIG. 3 is a sectional view somewhat similar to FIG. 2 except that thecutting tool electrode is the female member;

FIG. 4 is a schematic view of a control system for operating the EDMapparatus utilized to demonstrate the invention;

FIG. 5 is a view of the apparatus taken along line 5-5 of FIG. 4; and

FIG. 6 is a view of a modification.

Referring to the drawings in detail and initially to FIG. 4, theelectrical stock removal apparatus illustrated includes a cutting tool10 and a workpiece 12. The cutting tool 10 and the workpiece 12 as wellas the generation of time spaced electrical discharges across a. gap 14formed therebetween may be accomplished in any well known way, such asthat explained in the U.S. application Ser. No. 832,345 to Colten etal., filed Aug. 7, 1959, and entitled Electrical Discharge MachiningApparatus.

Because of this prior disclosure, this aspect will only be sucientlydetailed to facilitate an understanding of the invention. Briefly, apower supply denoted generally at 16 generates the electrical stockremoving discharges across a gap 14, these discharges taking place inthe presence of a suitable dielectric fluid. The voltage across the gap14 is sensed by a control circuit 20 where it is compared with areference voltage corresponding to the desired gap spacing. If there isa difference between the gap voltage and the reference voltage, thecontrol circuit 20 will produce a corresponding output signal. Thisoutput signal is employed by a force motor 22 for controlling aservomotor 24. The servomotor 24 can be of the rotary fluid pressureoperated kind and will cause a spindle 26 having the cutting tool 10drive connected thereto to be moved upwardly or downwardly through theagency of a gear 2S that engages a rack 30 formed on the spindle 26. Thespindle 26 is also revolved by an appropriate motor 32 at selectedspeeds, which may be established by adjusting the motor 32 in any knownway.

With the foregoing arrangement, any time the actual gap voltage variesfrom the predetermined reference gap voltage a correction in the gapspacing is made in order to achieve the optimum cutting gap. Also, ifpreferred, the workpiece 12 can be moved and the cutting tool maintainedstationary. This movement of the workpiece 12 would be by the same typeof mechanism, or both the cutting tool 10 and the workpiece 12 can beindividually maneuvered.

Very often is is found necessary to machine an opening 34 in theworkpiece 12 of a larger dimension than the cutting tool 10. This may bebecause the cutting tool 10 is unintentionally made undersize, or it ispreferred to use a smaller electrode because of the expense of thematerial, or it is wanted to reuse an electrode rather than prepare anew one. Normally, an electrode will make a certain size opening. Ifsubsequently, the size of the opening is to be increased, the pastpractice has demanded that a new oversize electrode be made. Forinstance, if the opening 34 is to have the configuration displayed bythe broken line in FIG. l, and the cutting tool 10 has the size and theshape shown by the solid line 36, it can be appreciated that there is asignificant dinerence in the sizes of the opening 34 and the size of thecutting tool 10.

To cut the opening 34 this amount oversize, the rotary motion of thespindle 26 is converted into translatory movement of a motion convertingmechanism denoted generally by the numeral 38. This translatory movementis defined as that motion in which all the points of a moving body haveat any instant the same velocity and direction of motion asdistinguished from rotation. The mechanism for accomplishing thisconversion includes an olset element as crank 40 appropriately driveconnected to the spindle 26. The axis of rotation of the crank 40 can bemade eccentric relative to the axis of rotation of the spindle 26 by ascrew 42 revolvably supported at the ends thereof by the spindle 26 andhaving mounted thereon the crank 40. Rotation of the screw 42 will causethe crank 40 to slide along a rotation inhibiting slot 43 as viewed inFIG. 4. This sliding movement, as observed in FIG. 4, will be either tothe left or to the right, a predetermined extent, determined by theonset wanted.

For purposes of demonstration, it will be assumed that the axis of thecrank 40 traverses the circle 44 shown in FIG. l, the point 46 being thecenter of rotation of the spindle 26. This rotary motion of the crank 40is transferred to the cutting tool 10 through primary and secondaryslides 48 and 50 and a roller bearing 52 interposed between the crank 40and the primary slide 48. As best observed in FIG. 5, rotation of thecrank 40 will, because of the roller bearing 52, cause the primary slide48 to which is connected the cutting tool 10, to also attempt torevolve. Because of the secondary slide 50, which is slidably mounted ina fixed bracket 54, the cutting tool 10 can only move left and right orup and down from the FIG. position` The combination of these movementswill cause the cutting tool to machine to the broken line in FIG. 1 astong as the radius of the onset circle 44 is set for this extent ofovereut.

If instead of an opening 34, it is now desired to machine a workpiece 12so as to form a protrusion on a punch or the like, such as in FIG. 3,the cutting tool 10' is utilized and the travel thereof is caused by themechanism 38 to be in the same directions mentioned in describing FIG.5. The amount of travel will be that required to machine to the brokenline on the workpiece 12' and this will correspond to the radius oramount of onset of the crank 40.

In FIG. 6, a modified motion converting mechanism 38' is depicted forproducing the translatory movement of the cutting tool 10. A plate 55may have the cutting tool 10 suitably joined thereto and may also havethe bearing 52 therein for receiving the crank 40. A shaft 56 is mountedon the plate 55 and has slidable thereon one end of link 58. At theopposite end, the link 58 is slidably joined to a cross shaft 60extending normal to the directionoftheshaft56andsecuredtoaiixedframe62-lf preferred, the cross shafts 56 and60 can be slidable and have the link 58 xed thereon or a combinationthereof. Also, as those skilled in the art will appreciate, approprietesliding ways (not shown) may be employed for moving the plate 55 and thefixed frame 62 relative to each other. One or more of these mechanisms38' may be employed. As with the coaction between the primary andsecondary slides 48 and 50 in the FIG. 4, embodiment, the cutting tooll0 can only travel in two coordinate directions that are normal relativeto each other. Hence, the cutting tool l0 cannot rotate with the crank40 but is required to have the previously referred to translatorymotion.

From the foregoing, it can be appreciated that with the mechanisms 38and 38', either an undersized male cutting tool 10 can be utilized tomachine an opening in a workpiece or an oversize female cutting 10 canbe employed to machine a punch or the like. Moreover, noncircularconfigurations can be formed While employing a rotating power source.

Another significant feature of the FIG. 4 apparatus is the provision formachining in different ways. First, if wanted, the cutting tool 10 canbe fed into the workpiece 12 the desired depth without any translatorymovement merely by setting the crank so as to have a zero eccentricityrelative to the spid In other words, the crank 40 and the spindle 26have no onset but are c0- axial or axially aligned. When at the desireddepth, the offset can be established and the oscillatory movement of thecutting tool 10 commenced without any change in the actual positions ofthe cutting tool 10 and workpiece l2. The opening 34 is then cut to thedesired size, the cutting taking place along the sides of the opening34. By dressing the sides of the cutting tool 10 so as to make themstraight, the movement of the cutting tool 10 into the sides of theopening 34 will insure that straight sides are generated.

Second, the desired offset can be established and the translatory motionof the cutting tool 10 caused to take place at the same time as thecutting tool 10 is fed into the workpiece 12. In this application, thefeeding of the cutting tool 10 by servomotor 24 and the rotation of thespindle 26 by the motor 32 is coordinated or synchronized byappropriately adjusting the speeds for the best results.

Third, the sides of the opening 34 can be tapered to any desired amountby adjusting the onset as the cutting tool 10 is fed into the workpiece12. The changing of the onset can be done manually by rotating the screw42 or automatically through a variable speed motor 63 that rotates ascrew shaft 64 carried inside the spindle 26 and made movable with thespindle 26. The motor 63 will through bevel gearing 66 cause the screw42 to be turned and the onset of the crank 40 changed. The operation ofthe motor 63 may be controlled by the control circuit 20 in any suitableway so as to commence the rotation thereof at an appropriate speed andat the same time as operation of the control circuit 20 commences toinitiate the feed of the spindle 26 and accordingly the cutting tool 10towards the workpiece 12.

The invention is to be limited only by the following claims.

We claim:

[1. In combination, a cutting tool member for machining a. workpiecemember, means feeding the members relative to each other, a rotatingdriver, and means converting the rotary movement of the driver intotranslatory movement of one of the members relative to the other, thetranslatory movement being in a plane transverse to the direction ofrelative movement between the members] [2. In combinatiop, a cuttingtool member for machining a workpiece member, a rotating driver, andmeans converting the rotary movement of the driver into translatorymovement of one of the members relative to the other so as to generate anoncircular pattem] 3. In combination, a cutting tool member formachining a workpiece member, a rotating input arranged to revolve aboutan onset axis, means drive connecting the input to one of the members,and means preventing rotation of the one member so that the one memberhas translatory movement about the onset axis.

4. In combination, a cutting toolmember for machining a workpiecemember, an input revolvable about a certain axis, an output driveconnected to the input and revolvableabout an axis offset relative tothe axis of the input, means connecting the output to one of themembers, and means preventing rotation of the one member so that the onemember is caused to have translatory movement about the offset axis.

5. In combination, a cutting tool member for machining a workpiecemember, a rotating driver, and means converting the rotary movement ofthe driver into translatory movement of one of the members, the rotarymovement converting means including means mounting the one member formovement in two coordinate directions.

6. In combination, a cutting tool member for machining a workpiecemember, a rotating input, an offset element revolvable by the inputabout an axis eccentric to the rotary axis of the input, and meansconverting the rotary movement of the offset element into translatorymovement of one of the members, the rotary movement converting meansincluding a revolvable connection between the one member and the offsetelement and means mounting the one member for movement in two coordinatedirections.

7. In combination, a cutting tool member for machining a workpiecemember, a rotating input, an offset element revolvable by the inputabout an axis eccentric to the rotary axis of the input, and meansconverting the rotary movement of the offset element into translatorymovement of one of the members, the rotary movement converting meansincluding a bearing connection between the offset element and the onemember, first means slidably mounting the one member for movement in onedirection and second means slidably mounting the one member for movementin a direction transverse to the movement of the first means.

8. In combination, a cutting tool member for machining a workpiecemember, a rotating driver, means feeding the members relative to eachother, an offset element revolvable by the driver about an axiseccentric to the axis of rotation of the driver, means adjusting theeccentricity, and means converting the rotary movement of the offsetelement into translatory movement of one of the members, the translatorymovement being in a plane transverse to the direction of relativemovement between the members.

9. In combination, a female cutting tool member for machining a maleworkpiece member, a driver revolvable about an axis, an offset elementrevolvable by the driver about an axis eccentric to the axis of rotationof the driver, and means converting the rotary movement of the osetelement into translatory movement of' one of the members, the rotarymovement converting means including a bearing connection between theoffset element and the one member and a pair of slides mounting the onemember for shiftable movement in coordinate directions.

10. In combination, a male cutting tool member for machining a femaleworkpiece member, a driver revolvable about an axis, an offset elementrevolvable by the driver about an axis eccentric to the axis of rotationof the driver, and means converting the rotary movement of the offsetelement into translatory movement of one of the members, the rotarymovement converting means including a bearing connection between theoffset element and the one member and a pair of slides mounting the onemember for shiftable movement in coordinate directions. Y

11. In combination, a cutting tool member for machining a workpiecemember, a driver revolvable about the axis thereof. an offset elementrevolvable by the driver about an axis eccentric to the axis of thedriver, means altering the position of the eccentric axis relative tothe axis of the driver, and means converting the rotary movement of theoffset element into translatory movement of one of the members so as tocause a certain configuration to be machined in the workpiece member,the rotary movement converting means including a bearing connectionbetween the offset element and the one member and a pair of slidesmounting the one member for shiftable movement in coordinate directions.

l2. In combination, a cutting tool member for machining a workpiecemember, means feeding the members relative to each other, a rotatingdriver, means converting the rotary motion of the driver intotranslatory movement of' one of the members relative to the othermember, means altering the translatory movement of the one member, andmeans coordinating the operation of the feeding means and the alteringmeans so as to produce a predetermined taper.

13. In electrical stock removal apparatus of a character in whichelectrical discharges are generated across an ionizable tiuid filled gapformed between cutting tool and workpiece electrodes sq a? to erodematerial from the workpiece electrode, `tho mbination comprising arotating driver, means feeding the electrodes relative to each other,and means converting the rotary movement of the driver into translatorymovement of one of the electrodes relative to the other of theelectrodes, the translatory movement being in a plane transverse to thedirection of relative movement between the electrodes.

14. In electrical stock removal apparatus of the character in whichelectrical discharges are generated across an ionizable fluid filled gapformed between cutting tool and workpiece electrodes so as to erodematerial from the workpiece electrode comprising a rotating driver, anoffset element re-volvable by the driver about an axis eccentric to theaxis of rotation of the driver, and means converting the rotary movementof the offset into translatory movement of the one of the electrodes,the rotary motion converting means including a revolvable connectionbetween the offset element and the one electrode and slide meansmounting the one electrode for movement in two coordinate directions.

15. In electrical stock removal apparatus of a character in whichelectric discharges are generated across an ionizable fluid filled gapformed between cutting tool and workpiece electrodes so as to causestock to be removed from the workpiece electrode comprising a rotatingdriver, an oset element revolvable by the driver about an axis eccentricto the axis of the driver, and means converting the rotary movement ofthe offset element into translatory movement of one of the electrodes,the rotary movement converting means including a bearing connectionbetween the one [member] electrode and the offset element, a first slidemounting the one electrode [member] for movement in one direction and asecond slide for mounting the one electrode for movement in anotherdirection.

16. In electrical stock removal apparatus of a character in whichelectrical discharges are generated across an ionizable fluid filled gapformed between cutting tool and workpiece electrodes so as to causestock to be eroded from the workpiece electrode comprising means feedingone of the electrodes relative to the other, a driver rotatable aboutthe axis thereof, an offset element revol'vable by the driver about anaxis eccentric to the axis of rotation of the driver, means altering theeccentricity of the offset element relative to the driver, meansconverting the rotary movement of the driver into translatory movementof one of the electrodes and means coordinating the operation of thealtering means and the feeding means so as to machine according to acertain scheme, the rotary movement converting means including arevolvable connection between the offset element and the one electrodeand means slidably mounting the one electrode for movement in coordinatedirections.

17. In electrical stock removal apparatus of the character in whichelectrical discharges are generated across an ionizable fluid filled gapformed between cutting and workpiece electrodes so as to cause stock tobe eroded from the workpiece electrode comprising means feeding theelectrodes relative to each other, a driver revolvable about the axisthereof, means convening rotary movement of the driver into translatorymovement of one of the electrodes, the translatory movement being in aplane transverse to the direction of relative movement lbetween theelectrodes, and means synchronizing the operation of the feeding meansand the rotation of the driver so as to cause stock to be removed fromthe workpiece according to a certain scheme.

18. In electrical stock removal apparatus of the character in whichelectrical discharges are generated across an ionizable fluid filled gapformed between cutting and workpiece electrodes so as to erode stockfrom the workpiece electrode comprising means feeding the electrodesrelative to each other, a rotating driver, means converting rotarymovement of the driver into translatory movement of one of theelectrodes, the translatory movement lbeing in a plane transverse to thedirection of relative movement between the electrodes, means altering thextent of translatory movement of the one electrode, and meanscoordinating the operation of the feeding means with the operation ofthe altering means so as to cause stock to be removed from the workpieceelectrode in accordance with a certain scheme.

19. In electrical stock removal apparatus of the character in whichelectrical discharges are generated across an ionizable iuid filled gapformed between cutting tool and workpiece electrodes so as to causestock to be eroded from the workpiece electrode comprising means feedingthe electrodes relative to each other, a driver revolvable about theaxis thereof, an olset element revolvable by the driver about an axiseccentric to the axis of rotation of the driver, means adjusting theeccentricity of the offset element relative to the axis of rotation ofthe driver, means converting the rotary movement of the olfset elementinto translatory movement of one of the electrodes so as to cause theworkpiece to be machined according to a certain scheme, the rotarymovement converting means including a bearing connecting the offsetelement and the one electrode and means slidably mounting the oneelectrode for movement in coordinate directions, and means coordinatingthe adiustment of the eooentricity of the oiset element with theoperation of the feeding means and the rotation of the driver so as tocause material to be removed from the workpiece electrode according to acertain scheme.

20. The method of producing a desired shape in or on o work member byelectrical erosion, the work member being formed of electricallyconducting material, comprising the steps of: positioning o shapedelectrode member with respect to the work member so that one of saidmembers encircles a portion of the other member and with the shapedportion of the electrode member adjacent the portion of the work memberto be shaped, causing relative orbital movement between the electrodemember and the work member without relative rotation or axial feed, andcausing an electric erosion current to fow between the electrode memberand the work member.

2l. The method of claim 20 wherein the electrode member is shaped on itsouter surface to form the desired shape on an inner surface of the workmember.

22. The method of claim 20 wherein the electrode member is shaped on aninner surface to form the desired shape on an outer surface of the workmember.

23. Apparatus for relatively moving an electrode element and a workpieceelement for electrically shaping the latter, comprising separate,approximately coaxial holding means for each of said elements, a firstone of said holding means and its related ope f said elements beinglinearly movable axially and sec 'd one of said holding means and itsrelated one of said elements being restrained against such linear, axialmovement, one of said holding meant comprising a first body memberrestrained against movement transversely of the line of said linearmovement, a second body member coaxially aligned with said first bodymember, a connection between said body members restraining them againstrelative rotary movement about said line and against relative movementin parallelism with said line, and actuating means for successivelymoving said second body member translationally to angu- Iarly spacedpoints in o plane perpendicular to said line whereby to enable saidelectrode element to form, on said workpiece element, a surfacesubstantially uniformly spaced from directly opposed surface portions ofsaid electrode element.

References Cited The following references, cited by the Examiner, are ofrecord in the patented file of this patent or the original patent.

UNITED STATES PATENTS 900,313 10/ 1908 Schutz 74-86 1,188,903 6/ 1916Cornwall 74-87 2,580,716 1/ 1952 Balamuth.

2,766,364 10/1956 Higgins et al. 2,773,968 12/ 1956 Martellotti et al.2,794,110 5/ 1957 Grith. 2,385,665 9/ 1945 Warwick. 2,773,968 12/1956Martellotti et al.

RALPH F. ST AUBLY, Primary Examiner U.S. Cl. X.R.

P04050 UNITED STATES PATENT OFFICE CERTIFICATE 0F CURRECTION Patent No.Re. 26,970 Dated Qctober 20, 11970 Inventods) Robert F. Bentley and SamV. Simonetti It is certified that error appears in the above-identifiedpatent and that said Letters Patent are hereby corrected as show-nbelow:

In ColumZ, line 7l, change "is" (first occurrence) to In Colunm 7, Claiml?, line l0, after "workpiece" insert electrode --z Claim 18, line 2l,after "th" insert the letter e Signed and sealed this 27th day of April1971.

(SEAL) Attest:

EDWARD M.FLETCHER,J'R. WILLIAM E. SCHUYLER, JR. Attesting OfficerCommissioner of' Patents

